This invention relates to a running speed detecting device for marine vessels and more particularly to an improved, simplified and highly accurate device for detecting the speed of a marine vessel.
There are a number of types of speed indicators employed for watercraft. These devices all operate on electrical principles and include either the propeller type wherein a propeller is mounted on the hull and rotates at a speed which will be related to the speed of the hull or of the magnetic current meter type. Such magnetic current meter type devices also are provided on the exterior of the hull and each system requires the provision of connecting wires for transmitting a signal from the sensor to a remotely positioned indicator. However, the accuracy of such devices depends on the effectiveness of the transmission of the electrical signal from the remotely positioned speed transducer to the speed indicator positioned in proximity to the watercraft operator. As a result, these devices tend to be inaccurate.
In order to improve the accuracy of watercraft speed indicators and in order to permit a device that can be used with a wide variety of watercraft, it has been proposed to utilize the water pressure as an indicator of speed. To this end, the hull is provided with a forwardly facing opening that receives the water pressure which will be dependent upon the speed of watercraft travel. A conduit then conveys the water pressure from the opening to a remotely positioned speed indicating device that incorporates a pressure transducer that outputs a signal indicative of water pressure. A converter circuit then converts this water pressure signal into a speed signal. An arrangement of this type is shown in the copending application entitled "Speedometer For Marine Vessels," Ser. No. 160,124, filed Feb. 25, 1988 in the name of Kazuhior Nakahama et al, which application is assigned to the assignees of this application.
Although the arrangement shown in the aforenoted copending application is extremely effective, it should be understood that atmospheric pressure and water pressure can vary and as such these variations will affect the accuracy of the speed signal.
It is, therefore, a principal object of this invention to provide an arrangement for sensing watercraft speed through sensing of the pressure of the water as the watercraft moves and adjusting the signal in response to ambient or base line conditions.